IBM 19 - Manual (Page 379)

1284 Parallel
The Centronics parallel interface supports two modes for 1284
bi-directional communication, nibble mode and byte mode:
In nibble mode, bi-directional communication between the printer
and the host is done in nibbles (four bits) with the low order nibble
sent first. A transfer of two nibbles is required for each byte of
information. In byte mode, bi-directional communication between
the printer and the host is done in bytes. The byte mode may be
used by the host device in a DMA (Direct Memory Access) mode
for more efficient operation.
When byte transfer is complete and there is no more data to
transmit, the host may do one of the following:
■ terminate and return to the compatibility mode.
■ stay in the HostBusy, Data Not Available phase.
■ set HostBusy Low, putting the interface into the idle phase.
If there is additional data, the host may do one of the following:
■ set HostBusy Low, indicating that the host can accept
additional data.
■ stay in the HostBusy, Data Not Available phase.
■ terminate and return to the compatibility mode.
Check your host documentation to see if the host is 1284
compatible.
Appendix B
T e c h n i c a l S p e c i f i c a t i o n s B - 1 5
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